Towards the integration of electric vehicles into the smart grid

Electric Vehicles (EVs) have high energy capacity and their anticipated mass deployment can significantly increase the electrical demand on the grid during charging. Simulation results suggest that for every 10 % increase in households operating 3 kW EV chargers in an uncontrolled way, there is a potential increase of peak demand by up to 18 %. Given the limited spare capacity of most existing distribution networks, it is expected that large-scale charging of EVs will lead to potential problems with regard to network capacity and control. This paper presents analysis of these problems and investigates potential means by which the particular features of EV batteries may be used to enable large-scale introduction of EVs without the need for wholesale upgrading of power grids. Smart charging, using a combination of controlled EV charging (G2V) and Vehicle to Grid (V2G), can significantly help. The results presented demonstrate the benefits of smart charging for the grid and consider the impact of grid support on the EV battery lifetime. Various factors that affect capacity degradation of Lithium ion battery (used to power EVs) are analysed and the impacts of G2V and V2G operation on battery capacity loss and lifetime are evaluated. Laboratory test results are provided to quantify the effects of the various degradation factors, and it is shown how these may be ameliorated to allow economic network support using EV batteries without incurring excessive battery degradation in the process.